This invention relates to a laser beam shaping device suitable for unifying the energy distribution pattern of a laser beam on the surface irradiated thereby, and more particularly to a laser beam shaping device which is suitable for forming a laser beam which, being uniform in energy distribution, can be effectively utilized in a wide range of technical fields in which a laser beam is used for surface treatment such as trimming, film removing, etching, hardening, and chilling or alloying by remelting surfaces, or joining, welding, and fusing.
A few examples of conventional laser beam shaping devices will be described with reference to FIGS. 12 through 15.
A first example of the conventional laser beam shaping device, as shown in FIG. 12, employs segment mirrors. More specifically, the laser beam shaping device 101 has a beam shaping mirror 104 in which segments mirrors 103 for reflecting a laser beam are arranged in matrix form. The laser beam 102b reflected from the beam shaping mirror 104 is applied to an irradiation surface 105. The segment mirrors 103 forming the beam shaping mirror 104 adjust the incident angle of the laser beam 102a so that the laser beam 102b applied to the irradiation surface 105 is uniform in energy distribution.
A second example of the conventional laser beam shaping device is as shown in FIG. 13. It is a beam shaping device 111 using a kaleidoscope. The device 111 comprises: a condenser lens for concentrating a laser beam 112a into a laser beam 112b; a kaleidoscope 114 having a reflecting wall 114a which reflects the laser beam 112b in a multiplex mode; and a focusing lens 115 for forming the output laser beam 112c of the kaleidoscope 114 into a laser beam 112 which is applied to the irradiation surface 116. The laser beam 112b passed through the condenser lens 113 is applied to the kaleidoscope 114, and reflected by the reflecting wall 114a in a multiplex mode. As a result, it is outputted as the laser beam 112c uniform in energy distribution by the kaleidoscope 114.
FIG. 14 shows a third example of the conventional laser beam shaping device, a beam shaping device 121 of beam oscillation type. The device 121 comprises: a condenser lens 123 for concentrating a laser beam 122a to form it into a laser beam 122b; a reflecting mirror 124 for reflecting the laser beam 122b to output it as a laser beam 122c; a scanning reflecting mirror 125 for deflecting the laser beam 122c in a scanning manner so as to be applied, as a laser beam 122d, to the irradiation surface 127; and a scanner 126 for controlling the operation of the scanning reflecting mirror 125. The laser beam 122c reflected from the reflecting mirror 124 is applied to the scanning reflecting mirror 125, while the latter 125 is controlled by the scanner 126, so that the laser beam 122c is deflected in a scanning manner; that is, the laser beam 122d is applied to the irradiation surface 127 in an oscillation mode.
A fourth example of the conventional laser beam shaping device, as shown in FIG. 15, is a laser beam shaping device using a polygon mirror. The device 131 comprises: a focusing reflecting mirror 133 for reflecting a laser beam 132a and simultaneously focusing it into a laser beam 132b; and a polygon mirror 134 for deflecting the laser beam 132 in a scanning manner so that it is applied, as a laser beam 132c, to the irradiation surface 135. The laser beam 132b is applied to a reflecting mirror 134a of the polygon mirror 134 which is kept rotated in the direction of the arrow A. As the polygon mirror turns, the reflecting mirror 134a is also turned, so that the laser beam 132c is deflected in the direction of the arrow B. Thus, the irradiation surface 135 is repeatedly irradiated by the laser beam.
In the conventional laser beam shaping device 101 shown in FIG. 12, the beam shaping mirror 104 made up of a number of segment mirrors 103 arranged in matrix form is used. Therefore, it requires complex manufacturing techniques, and it is accordingly high in manufacturing costs. Furthermore, the configuration of the laser beam 102b applied to the irradiation surface 105 cannot be changed without replacing the segment mirror 103. In addition, it should be noted that there are gaps between the segment mirrors 103, which lowers the factor of reflection of the laser beam 102a, and increases the energy loss.
In the conventional laser beam shaping device 111 using the kaleidoscope 114 shown in FIG. 13, the laser beam 112b is reflected in the kaleidoscope 114. However, its incident angle to the reflecting wall 114a being large, the absorption of the P polarization component by the reflecting wall 114a is large accordingly, resulting in an increase in the energy loss by the multiple reflection at the reflecting wall 114a. Since the beam configuration is determined by the configuration of the reflecting wall 114a of the kaleidoscope 114, it is rather difficult to change the beam configuration.
In the conventional laser beam shaping device of beam oscillation type shown in FIG. 14, it is difficult to deflect the laser beam at high frequency in a scanning mode, and accordingly it is difficult to obtain a laser beam 122d over the irradiation surface 127 which is uniform in energy distribution. In addition, the scanner 126 itself is not high enough in durability.
The fourth example of the conventional laser beam shaping device, using the polygon mirror as shown in FIG. 15, is also disadvantageous in that, when defocused, the irregularity in mode of the laser beam 132a adversely affects the machining capacity, and therefore it is necessary to make the spot diameter of the laser beam small to oscillate the latter. In addition, it is difficult to maintain the durability of the driving means and adjust the alignment.
In each of the first through fourth examples of the conventional laser beam shaping device, the reflection of the laser beam at the irradiation surface results in a large energy loss thereof, and it is therefore necessary to form a coating on the irradiation surface to increase the absorption of the laser beam.